Win2003 network problems after some time...

I have Windows 2003 server and ADSL 2Mb/s internet connection. Also I have a LAN with 2 XP computers, only one laptop (sometimes appears in network).
Also I have licensed Agnitum Outpost Firewall 2.1 on this win2003 server + some plugins.
Usually I download some working data from ftp servers and so on... Then I have a very strange problem: when I reboot server and dial DSL, internet connection works very fine - very quick, I can connect to all my ftp and mail, but after some time, perhaps 3-4-5 hours, internet become very slow, connections are slow, I.E. opens pages very long, I can't connect to my ftp's and mail servers, but, if I was previously connected to some ftp, speed stay good.
I can't find what the problem is, but I mentioned, if I am not using inet at all it stays in good speed. Before, when in my server was Win XP I didn't have such problems.

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Update all antivirus and run full scans. Run spyware scans with Adaware and SpyBot. Sounds like a virus.

NeolitenAuthor Commented: 2004-08-12

Well, I have realtime file protection from Norton Antivirus 2004 and I just scanned my computer - it's nothing. I also have Ad-aware software and it's clean. I used SpyBot and it found only one DSO Exploit... I will see then, will inet slow down or not..

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Yes, I always have firewall on and I analyse logs sometimes. What I should see in this logs? By my view it's nothing wrong with them: no DDOS attacks or something like that. I have dynamic IP address, so if I reconnect, my IP will change, and to attack whole my network - quite impossible.

But can it be, that I have too much outgoing connections and this will kill my connection? Now I have 30 outgoing connection according my firewall, but this value is small.

Why dont you just have someone with some shell space nmap your connection, use this as a small firewall audit. Netstat -an from dos should give you some good information too.

I take it your adsl is PPPOE because you said dial in. What happens if you disconnect and reconnect with PPPOE without rebooting?
Have you tried restricting your outgoing open ports? This is a good practice, and most home users have no use for outgoing ports. Even if your running
a mail and webserver you only need 4 ports.

I wouldnt jump to conclude that this is indeed a virus/trojan problem. You will need some sort of traffic monitoring. I am very familar with this on *BSD based systems, but I am unsure how to go about it on a windows system. I know in the performance monitor you can set it to watch the traffic on your network card. That might be your best bet. Capturing broadcast traffic would be even better, but it doesnt sound like you have an easy way to do that.\

I just meant it sounded like a virus - not that it was. I was only proposing a possibility, not diagnosing the cause.

NeolitenAuthor Commented: 2004-08-12

As far as I know, when I disconnect and reconnect the problem is still present, inet only become working properly after reboot. What things can produce this sort of problems with my inet? and I restrict my outgoing ports with Outpost Firewall, what ports usually windows using or software using??
Thank you for information, I will try to monitor my traffic and after I will submit the results.

What about restarting the services in the administrative tools that are related to INET?
Cant look them up atm, out of time for now.

NeolitenAuthor Commented: 2004-08-12

Thank you for this list, and what about changing MTU value? Could someone explane, what exactly is this value?
I slightly reduced this value and it seems that inet become more stable - 30 hours + high loading. I also block some ports, so it could be solution too.